1) Field of the invention
The present invention relates to a technology for recycling the wash residue of ready mixed concrete or mortar (hereinafter ready mixed concrete, etc.) occurring as a result of washing conveyors or plant mixers in concrete mixing plants. More particularly, the present invention relates to a technology for preparing new ready mixed concrete, etc. by measuring the unhydration ratio of cement contained in the condensed sludge obtained from the wash residue of ready mixed concrete, etc., and then adding a predetermined amount of said condensed sludge to a new batch of ready mixed concrete.
2) Description of the Related Art
The wash residue of ready mixed concrete occurring in ready mixed concrete plants, etc. is high in alkaline value and contains toxic substances such as hexavalent chrome, and is therefore usually discarded and buried in remote areas.
Such wash residue is conventionally discarded because it will deteriorate the strength of concrete and increase the drying shrinkage when mixed with a new supply of ready mixed concrete.
The applicant of this invention proposed a method and system of recycling the wash residue of ready mixed concrete which can manufacture high quality concrete by taking out cement unhydrates from the wash residue without drying and mixing the unhydrates with a new batch of ready mixed concrete to thereby efficiently recycle resources (Japanese Patent Application laid-open Sho 62-204867).
According to this method of recycling, the wash residue is first classified in a wet process by a classifier, and the aggregates such as sands and gravels are removed to obtain cement sludges. The cement sludge is then condensed by a condenser, and concentration of the condensed sludge is further increased by a condensation tank to thereby obtain the cement sludge controlled to a predetermined concentration. The cement sludge is then crushed into fine particles with a vibrating ball mill to obtain a sludge containing fine sludge particles as the disperse phase on the surface of which cement unhydrates appears.
The wash residue of used ready mixed concrete, etc. decreases in its unhydration ratio of cement depending on its age. If the amount of sludge to be admixed with new supply of concrete, etc. is determined uniformly by assuming that the unhydration ratio of cement contained in the sludge which has been crushed as mentioned above is constant, there occurs such inconveniences as fluctuation in strength or drying shrinkage when the new batch of ready mixed concrete, etc. becomes hardened.